Casting procedure



Nov. 14, 1944. E. H. ZAHN y CASTING PROCEDURE Fiied June s, 1945 FE1 l INVENTOR ATTORNEY Patented Nov. 14, 1944 UNITED STATES .PATENT ori-lcs CASTING PROCEDURE t Application June 3, 1943, Serial No. 4893425L 3 Claims.

terized by their extreme hardness and toughness.v

These qualities, and others, such as resistance to corrosion and to chemical action, make them ptentially useful for the manufacture of a large variety of different articles, but some of the very qualities which make these materials desirable for use raise special manufacturing dilculties. For example, certain alloys are so hard that they cannot feasibly be machined, drilled, or otherwise worked, and they are therefore of practical utility only if the articles to be made can be produced by a casting operation. If the cast article is to have an interior cavity or bore, a casting procedure involving the use of a core or cores must be resorted to. And where the bore is of fine dimensions (by which term I refer, for example, to diameters of minute fractions of' an inch), unusual problems are encountered. A primary object of the present invention is to provide an entirely practical and commercially-useful solution to these special problems.

Where a cast article is to have an interior cavity of fine dimensions, ordinary casting cores and core-removing techniques cannot; usually be used. The core must obviously be of relatively delicate character and accurate dimensions, yet it must be adequately strong to remain intact and retain its shape during the casting procedure; it must be heat-resistant; and it must be capable of 'removal in a practical manner after the casting has been made.

My present invention is predicated upon the discovery that these desired qualities may be found to best advantage in an extruded or drawn element of metal or other material, suchy as a nickel wire, a quartz filament, or a length of ceramic tube; and one of the features of my invention resides in the removal of the core from the finished casting by dissolving it. For example, a drawn nickel- Wire is of uniform size and reasonably strong, its melting point is high enough to withstand the temperatures of most casting procedures ,and it may be removed by the dissolving action of nitric acid or its aquivalent. A drawn quartz filament has the added advantage of being highly refractory and unusually resistantl to heat shock; and it may beremovedby hydrouoric acid or its equivalent. An extruded ceramic tube is unusually good for the purpo-se not only because of its strength and rigidity and its smooth outer surface and uniform exterior diameter, but because its hollow nature facilitates the introduction into it of hydrofluoric acid, lye, caustic soda, or other'equivalent agentor the purpose of dissolving it away after the casting has been completed.

By the term dissolving as used herein and in the appended claims, I intend to refer to any destructive chemical action analogous to true dissolution, as distinguished from conventional core-v removing procedures involving physical disruption or withdrawal, or core-melting by means of heat. The use of a hollow core and its ultimate removal by the introduction into it of something which dissolves it is itself a procedure which I believe to be newk and which may obviously have wider utility per se in the casting art generally.

While the present invention is not necessarily limited to the casting of any particular metal or alloy, nor to the manufacture of any particular type or kind of article, its general nature is well exemplified by the procedure I have herein chosen to yillustrate and describe, relating to the manufacture of a bile duct tube. Such an article is illustrative of numerous items intended for permanent surgical implantation in the human body, for which a hard, durable, non-corrodible alloy, such as a chromium-cobalt-molybdenum alloy, is particularly well adapted; and since a bile duct tube must necessarily have a fine bore through it, it is Well suited to serve as an illustration of the features ofthe present invention.

In the accompanying drawing:

Figure 1 is an exploded view of an illustrative bile duct tube and the manner in which it is generally used;

Figure 2 is a cross-sectional view through a cored casting mold in which the bile duct tube of Figure 1 may be produced;

Figure 3 is a perspective view of the casting produced in the mold of Figure 2 prior to the final removal of the core; and

Figure 4 is a cross-sectional view taken substantially along the line 4-4 of Figure 3.

A bile duct tube is a small thin-walled tubular element, possibly one-half an inch or so in length, having an outer diameter generally not exceeding about one-eighth of an inch. -It may be used, for example, to connect together two opposed portions of the human bile duct after a diseased or injured intermediate portion has been surgically removed. An illustrative tube of this character is shown in Figure 1 and designated by the reference numeral I0. Its opposite ends are designed for insertion into the opposed ends Il of the human bile duct Whose continuity is to be reestablished. Generally, annular grooves I2 are formed in the tube Ill near its ends to facilitate the application of sutures, and it is customary practice to provide the tube I0 with a medial projecting n I3 by means of which additional sutures may be employed to anchor the tube in proper position within the body.

Iir such a tube is to be made of a non-corrodible metallic alloy, such as a chromium-cobalt-molybdenum alloy, it must be cast, and a core must be employed to provide for the nne longitudinal bore which extends through the tube. In Figure 2, I have illustrated the essential features of a casting mold which may be employed for this purpose. 'I'his mold is preferably a one-piece mold Il provided with the casting cavity I and one or more sprues I6 through which the molten metallic alloy is` to be introduced. A core is associated with this mold, and I have illustratively shown a core I1 in the form of a drawn or extruded length of ceramic tube.

After the metal has been cast, the mold is destroyed and the resultant casting and core are removed and appear as shown in Figure 3. The core I1 is then removed by dissolving it out. This may be accomplished in any of a variety of ways, for example, by immersing the assembly of Figure 3 in a bath of material which has a dissolving eect upon the core I1. The ability of this dissolving material to enter into the interior of the core I1, by virtue of the hollow nature of this core, facilitates the dissolving action.

After the core has been removed, it remains only to clean and polish the resultant casting.

The mold shown in Figure 2 is illustrated in a somewhat'diagrammatic fashion, and it will be understood that the mold may partake of any desired exterior shape or structure depending upon the requirements of the commercial procedure to be followed. For example, for the sake of simplicity of illustration, I have omitted to show the details of the casting cavity whereby the iin I3 may be provided for, since such details are well known per se.

In actual practice, the complete manufacture and procedure might consist, for example, of the following steps: A model of the desired article (one of the finished articlesV may serve for this purpose) is mounted' on the core I1. By means of this assembled pattern, a set of permanent casting mold sections are produced, and this procedure may be carried out, for example, in the manner illustrated and described in Patent No. 2,306,516. The original model is then removed from the core and the core reinserted into this set of permanent mold sections. Molten wax is then poured into the mold to form a composite pattern with which the core I1 is associated. This pattern is then invested in the material of which the nal casting mold I4 is to be made. This material may be of any suitable refractory character, and after it has set it is subjected to heat in order to melt out the Wax portion of the pattern. 'Ihis results in producing the casting mold assembly as shown in Figure 2. Where the final casting is to be made of chromium-cobaltmolybdenum alloy or the like, the mold is then preheated to approximately 2000 F. and the molten alloy (usually at a temperature of `about 2800 F.) is forced into the mold cavity under pressure.

The permanent sectional mold may be used repeatedly to produce any desired number of composite wax patterns with each of which one of the present cores is associated, and each of which is adapted to be used in forming a separate refractory mold, as shown in Figure 2, for receiving the final casting. It may be desirable to make the permanent sectional mold of such a character that a plurality of composite wax patterns may be made in it at one time.

or a quartz filament or any other equivalent material of comparable strength, smoothness, uniformity and susceptibility to ultimate destruction by a dissolving action, the process is substantially the same. However, unless the coreN is hollow it is obviously impossible to introduce the dissolving material to the interior of the core, and I therefore prefer `to use a hollow type of core. Be that as it may, the use of a core, whether hollow or not, which is ultimately eliminated by dissolving it, permits the manufacture by a pure casting procedure, and without subsequent drilling, of numerous articles in which there are one or more cavities or b ores of relatively fine dimensional characteristics. My invention is therefore of obvious utility in a large variety of different arts and is by no means restricted to the manufacture of bile duct tubes or other items for use Within the human body. For example, many Where the core is composed of a nickel Wire metallic products having fine bores therein have heretofore required the employment of metal of relatively soft drillable quality so that the bores could be produced by drilling, whereas such items may now be cast of hard and tough metal notwithstanding the requirement that one or more fine bores having .diameters possibly as small as one thousandth (.001) of an inch be formed therein.

In general it will be understood that the present drawings and description are purely illustrative of the general nature of my invention, and that the details herein described and illustrated are given merely by way of example. It is therefore obvious that these details may be varied in numerous ways by those skilled in the general art of casting, and that the invention may be applied to a large variety of different purposes, all without departing from the spirit and scope of the invention as expressed in the appended claims.

Having thus described my invention and illustrated its use, what I claim as new and desire to secure by Letters Patent is:

l. A method of casting a metallic article with a ne bore therein, which consists in forming the casting around a core and then removing the core by dissolving it, said core consisting of an extruded or drawn quartz element of form-retaining refractory material having a smooth outer surface and an accurately uniform exterior diameter.

2. A method of casting a metallic article with a fine bore therein, which consists in forming the casting around a core and then removing the core by dissolving it, said core being composed of a quartz iilament and being dissolved by hydrofluoric acid or its equivalent.

3. The method of making an article having a fine bore therein of a high-melting-point metallic alloy which is castable but too hard for drilling, which consists in casting the alloy in a refractory mold in which a drawn quartz filament is mounted in predetermined position to define the fine bore ultimately desired, and thereafter removing said filament from the casting by subjecting it to the dissolving action of a material which is unreactive toward said alloy, the high lmelting point of said quartz filament and its inherent strength and resistivity to heat shock serving to maintain the filament intact during the casting procedure, whereby the desired bore is accurately produced in the resultant article.

ERIC H. ZAHN. 

